Related to #208.
* spot/twaalgos/dot.cc: Fix missing definitions of universal nodes,
and inclusion of universal nodes inside of SCC when none of the
destination comes back to the SCC.
* tests/python/_altscc.ipynb: Adjust and add more test cases.
* tests/core/alternating.test, tests/core/neverclaimread.test,
tests/core/readsave.test, tests/core/sccdot.test,
tests/python/decompose.ipynb: Adjust test cases.
* NEWS: Mention the bug.
and call it after parsing
* spot/twa/twagraph.cc, spot/twa/twagraph.hh
(twa_graph::merge_univ_dests): New method.
* spot/parseaut/parseaut.yy: Call it.
* spot/twaalgos/dot.cc: Improve output, now that
several edges can use the same universal destination.
* tests/core/alternating.test, tests/core/complete.test,
tests/core/parseaut.test, tests/python/_altscc.ipynb,
tests/python/alternating.py, tests/python/alternation.ipynb: Adjust
test case.
* doc/org/tut24.org: Adjust example.